Now, it's the first time I deal with RF circuits, so it's being a little troublesome since I don't really know where i start from. I just wanted to ask you some questions first:

-This architecture looks (to me, I can obviously be wrong) a little different from the ones I found in books, and it would be great if someone could explain it to me or direct me to a good source to understand it.
-The goal should be to substitute the transistor, which is obsolete, with one of my choice: I think that picking an Infineon transistor suited for this band would be good but again, I am not sure. Furthermore, I should try to lower the Vtune signal, which in the application note goes from 0 to 30 V, so I guess I should change the varicaps.
-After this, I know that my workflow should be to perform an open loop analysis of the circuit to see if it meets the requirements to oscillate (i.e. gain, phase shift), but again, not sure about that.